So-called biomass ethanol, which is obtained by producing ethanol by a fermentation method from a biomass used as a starting material, has been gaining attention in view of carbon neutrality. Herein, the term “biomass” is defined as referring to renewable and biological organic resources except for fossil resources. In particular, a woody biomass has been also used as a starting material for ethanol production. Representative examples of a woody biomass include rice straw, rice husks, food waste, livestock excretion, woodchips, firewood, wood charcoal, chips, pellets, briquettes, lumbar chips, sawdust, tree bark, and construction debris.
A woody biomass mainly contains cellulose as a carbon source. When ethanol production is carried out using a woody biomass as a starting material, cellulose is first saccharified with cellobiohydrolase such that cellobiose, which is a disaccharide, is obtained. Saccharomyces cerevisiae, which is generally used for ethanol production by a fermentation method, cannot directly produce cellobiose. Therefore, glucose obtained by degrading cellobiose with β-glucosidase is used for fermentation. Specifically, conventional ethanol production with the use of a woody biomass requires a two-stage saccharification step in which cellulose is first formed into cellobiose and then cellobiose is formed into glucose. Accordingly, ethanol production with the use of a biomass containing cellulose, such as a woody biomass, is more costly than ethanol production using a different biomass, and further it comprises complicated production steps.